The primary consumer needs which underlie development in the absorbent article field, in particular catamenials is a high protection and comfort level.
One highly desirable means of improving the comfort of absorbent articles is the use of so called `breathable backsheets`. Breathable backsheets may comprise an apertured formed film having directional fluid transfer as disclosed in for example U.S. Pat. No. 4,591,523. Such apertured breathable backsheets are typically vapour and air permeable allowing gaseous exchange with the environment. This thereby allows for the evaporation of a portion of the fluid stored in the core and increases the circulation of air within the absorbent article. This is particularly beneficial as it reduces the sticky feeling experienced by many wearers during use, particularly over extended periods of time.
However, the main drawback associated with the use of breathable backsheets in absorbent article is the increased probability of leakage, commonly referred to as wet through onto the users garment. Although such breathable backsheets in principle only allow the transfer of materials in the gaseous state and only one directional fluid transfer, physical mechanisms such as extrusion, diffusion and capillary action may still occur and result in the transfer of the fluids in the opposing direction through the backsheet and onto the users garments. In particular, these mechanisms become more dominant if the product is utilised during physical exertion, for heavy discharge loads or over extended periods of time. In effect, while breathable backsheets provide excellent comfort improvements they result in an unacceptable level of failure with regard to protection, especially under stressed conditions.
The problem of wet through onto users garments due to the incorporation of such breathable backsheets in absorbent articles has been recognized in the art. Attempts to solve the problem have mainly resided in the use of multiple layer backsheets such as those illustrated in U.S. Pat. No. 4,341,216. Similarly unpublished European patent application no. 94203230 discloses breathable absorbent articles comprising a breathable backsheet consisting of at least two breathable layers which are unattached to one another over the core area. Also unpublished European patent application no. 94203228 discloses a breathable backsheet for disposable absorbent articles comprising an outer layer of a gas permeable, hydrophobic, polymeric fibrous fabric and an inner layer comprising an apertured formed film having directional fluid transport.
Alternatively, another proposed solution to the problem has been to increase the thickness of the absorbent articles, which is usually achieved by increasing the core thickness in order to ensure the desired protection level.
However, none of the above solutions have proved fully satisfactory. This is particularly the case for thin products, as thickness is also considered as a key variable affecting product comfort. Thus, there exists a dichotomy in the methods available to provide increased comfort absorbent products, such that thin breathable products cannot provide the desired level of protection.
As a result, there exists a need to provide an absorbent article which offers improved comfort by the employment of a breathable backsheet and having a reduced thickness which maintains the required level of protection.
It has now been found that breathable backsheets may be utilised in thin sanitary napkins, thereby providing both a high level of protection and comfort by creating a hydrophobicity gradient between the backsheet and the core, achieved by the utilisation of a low surface energy material such as silicone and chlorofluorocarbons or a low surface energy treatment. In this manner it is believed that the physical mechanisms such as diffusion and capillary action are hindered and wet through is considerably reduced if not completely eliminated
A further advantage of the present invention is that, since it allows to provide breathable backsheets coated with the hydrophobic material, it is no longer necessary that this layer be entirely synthetic and it may be at least partially naturally derived. This provides an important consumer noticeable benefit as the product imparts a more natural feel to the touch.
The use of surface energy gradients as such is discussed in unpublished U.S. application Ser. No. 08/442,935. It discloses fluid transport webs, e.g. topsheets, which exhibit surface energy gradients. The web facilitates fluid transport in one direction and resists transport in the opposite direction. The web comprises first and second surfaces, which are separated from one another by an intermediate portion. The first surface of the web has a lower surface energy than the surface energy of the intermediate, thereby creating a surface energy gradient. Suitable low surface energy materials include silicone, fluoropolymers and paraffins. The web is particularly suited as a topsheet for absorbent articles in order to transport fluid away from the wearer-contacting surface into the absorbent structure.